Lung cancer remains the leading cause of cancer death among men and women in the U.S., with rates in women increasing 6-fold in recent decades. Furthermore, the majority of lung cancer cases in nonsmokers occur in women. Results from several epidemiological studies suggest that, in addition to tobacco smoke, estrogen may contribute to lung cancer risk and progression. Although receptor-mediated signaling pathways have been well studied in carcinogenesis, much less attention has been given to the potential contribution of estrogen metabolizing enzymes to tumor formation and progression. The goal of the present study is to use novel animal models to assess the impact of alterations in estrogen metabolism on lung cancer development. Rationale for this experimentation is provided by preliminary data that indicate for the first time that estrogen is metabolized within murine lung tissue. Exposure of mice to tobacco smoke induces the expression of cytochrome P450 1B1 (CYP1B1), an enzyme that converts both estrogen and constituents of tobacco smoke to carcinogenic derivatives. CYP1B1 expression is elevated in lung tumors vs. adjacent normal tissue, and levels of 4-hydroxyestrogen (4-OHE), a genotoxic estrogen metabolite produced primarily by CYP1B1, are elevated significantly within the murine lung following smoke exposure. The hypothesis of the proposed study is that inhibition of CYP1B1 will lead to decreased production of 4-OHE and provide protection against lung cancer; thus representing a novel molecular target for the chemoprevention of this disease. This hypothesis will be tested using the clinically relevant LSL-KrasG12D mouse model of lung tumorigenesis, CYP1B1-/- mice and novel double transgenic LSL- KrasG12D/CYP1B1-/- mice that have been established recently by this group. The impact of CYP1B1 deletion on estrogen metabolism within the lung will be examined in Specific Aim 1 by comparing the expression of genes involved in estrogen metabolism and estrogen metabolite profiles in lung tissue of female CYP1B1-/- and CYP1B1+/+ mice. In Aim 2, the feasibility of inhibiting CYP1B1 as a strategy for lung cancer prevention will be investigated using the LSL-KrasG12D mouse model. Inhibition of CYP1B1 will be achieved by gene deletion or administration of 2,3',4,5'-tetramethoxystilbene (TMS), a synthetic analog of resveratrol that is a selective inhibitor of CYP1B1. The effects of CYP1B1 inhibition on change in total tumor burden (tumor volume as determined by MRI) and tumor stage will be determined. Data obtained from the proposed studies are anticipated to reveal the potential utility of CYP1B1 as a molecular target for chemoprevention and provide novel insight into the contribution of estrogen metabolism to lung cancer development.